Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video coding. In some examples, an apparatus includes processing circuitry that stores reconstructed samples of a reconstructed block in a memory. When a current sub-block in a current block is to be reconstructed using intra block copy (IBC) based on a reference sub-block in the reconstructed block, the processing circuitry determines whether the reconstructed samples of the reference sub-block stored in the memory are indicated as overwritten based on a position of the current sub-block, generates reconstructed samples of the current sub-block based on the reconstructed samples of the reference sub-block when the reconstructed samples of the reference sub-block stored in the memory are determined to be indicated as not overwritten, and overwrites the reconstructed samples of a collocated sub-block in the reconstructed block stored in the memory with the generated reconstructed samples of the current sub-block.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/735,002, “Reference search rangeoptimization for intra picture block compensation” filed on Sep. 21,2018, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus includes processingcircuitry that stores reconstructed samples of a reconstructed block ofa picture in a memory. The reconstructed samples of the reconstructedblock are reconstructed according to an encoded video bitstream. When acurrent sub-block in a current block of the picture is to bereconstructed using intra block copy (IBC) based on a referencesub-block in the reconstructed block, the processing circuitrydetermines whether the reconstructed samples of the reference sub-blockstored in the memory are indicated as overwritten based on a position ofthe current sub-block, generates reconstructed samples of the currentsub-block for output based on the reconstructed samples of the referencesub-block when the reconstructed samples of the reference sub-blockstored in the memory are determined to be indicated as not overwritten,and overwrites the reconstructed samples of a collocated sub-block inthe reconstructed block stored in the memory with the generatedreconstructed samples of the current sub-block.

In some embodiments, the current block includes one or morenon-overlapping partitions, including a current partition in which thecurrent sub-block is located, and the reconstructed block includes oneor more non-overlapping partitions that are collocated with the one ormore partitions of the current block, respectively. In some embodiments,the processing circuitry determines the reconstructed samples of thereference sub-block stored in the memory are indicated as notoverwritten, when the partition in the reconstructed block that includesthe reference sub-block is collocated with one of the partitions in thecurrent block that has not been reconstructed.

In some embodiments, the current block has a size of 128×128 lumasamples, and the one or more partitions of the current block includesfour partitions each having a size of 64×64 luma samples.

In some embodiments, the one or more partitions of the current blockinclude only one partition that is a size of the current block. In someembodiments, each of the one or more partitions of the current block hasa size that is equal to or greater than a maximum reference sub-blocksize used in the IBC.

In some embodiments, the current block includes upper-left, upper-right,lower-left, and lower-right partitions, and the reconstructed blockincludes upper-left, upper-right, lower-left, and lower-rightpartitions. In some embodiments, the processing circuitry determines thereconstructed samples of the reference sub-block stored in the memoryare indicated as not overwritten when the current sub-block is locatedin the upper-left partition in the current block, and the referencesub-block is located in one of the upper-right, lower-left, andlower-right partitions in the reconstructed block. In some embodiments,the processing circuitry determines the reconstructed samples of thereference sub-block stored in the memory are indicated as notoverwritten when the current sub-block is located in the one of theupper-left, upper-right, and lower-left partitions in the current block,and the reference sub-block is located in the lower-right partition inthe reconstructed block.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of a current block in a currentpicture to be coded using intra block copy (IBC) in accordance with anembodiment.

FIG. 9 is a schematic illustration of a current block and a neighboringblock in a current picture using IBC in accordance with an embodiment.

FIG. 10A is a schematic illustration of how reconstructed samples in aneighboring block are to be indicated as overwritten based on a positionof a current sub-block that is coded using IBC in accordance with oneembodiment.

FIG. 10B is a schematic illustration of how reconstructed samples in aneighboring block are to be indicated as overwritten based on a positionof a current sub-block that is coded using IBC in accordance withanother embodiment.

FIG. 11 is a schematic illustration of a current block, a firstreference block, and a second reference block between the current blockand the first reference block in a current picture using IBC inaccordance with an embodiment.

FIG. 12 shows a flow chart outlining a decoding process (1300) accordingto an embodiment of the disclosure.

FIG. 13 shows a flow chart outlining an encoding process (1400)according to an embodiment of the disclosure.

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers, and smartphones, but the principles of the present disclosure may be not solimited. Embodiments of the present disclosure find application withlaptop computers, tablet computers, media players, and/or dedicatedvideo conferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230), and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks, and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs), andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

FIG. 8 is a schematic illustration of a current block (810) in a currentpicture (800) to be coded using intra block copy (IBC) in accordancewith an embodiment.

In some examples, a block may be coded using a reference block from adifferent picture, which is also referred to as motion compensation. Insome examples, a block may be coded using a reference block from apreviously reconstructed area within the same picture, which is alsoreferred to as intra picture block compensation, current picturereferencing (CPR), or intra block copy (IBC). A displacement vector thatindicates the offset between the current block and the reference blockis referred to as a block vector (or BV for short). Different from amotion vector in motion compensation, which can be at any value(positive or negative, at either x or y direction), a block vector issubject to constraints to ensure that the reference block has alreadybeen reconstructed and the reconstructed samples thereof are available.In some embodiments, in view of parallel processing constrains, areference area that is beyond a tile boundary or wavefront ladder shapeboundary is also excluded.

The coding of a block vector can be either explicit or implicit. In theexplicit mode, the difference between a block vector and its predictorcan be signaled in a manner similar to an AMVP mode in inter coding. Inthe implicit mode, the block vector can be recovered from a predictor,in a similar way as a motion vector in merge mode. The resolution of ablock vector, in some implementations, is set to integer positions or,in some examples, to fractional positions.

The use of IBC at the block level can be signaled using a block levelflag. In some examples, this flag can be signaled when the current blockis not coded in merge mode. In some examples, this flag can be signaledby a reference index approach. This is done by treating the currentdecoded picture as a reference picture. In HEVC Screen Content Coding(HEVC SCC), such a reference picture is placed in the last position ofthe list. This special reference picture is also managed together withother temporal reference pictures in the Decoded Picture Buffer (DPB).

There are also some variations for implementing IBC, such as flippedintra block copy (where the reference block is flipped horizontally orvertically before being used to predict current block), or line basedintra block copy (where each compensation unit inside an M×N codingblock is an M×1 or 1×N line).

An example of using IBC is shown in FIG. 8, where the current picture(800) includes 15 blocks arranged into 3 rows and 5 columns. In someexamples, each block corresponds to a Coding Tree Unit (CTU). Thecurrent block (810) includes a sub-block (812) (e.g., a coding block inthe CTU) that has a block vector (822) pointing to a reference sub-block(832) in the current picture (800).

The reconstructed samples of the current picture can be stored in adedicated memory. In consideration of implementation cost, the referencearea where the reconstructed samples for reference blocks remainavailable may not be as large as an entire frame, depending on a memorysize of the dedicated memory. Therefore, for a current sub-block usingIBC, in some examples, an IBC reference sub-block may be limited to onlycertain neighboring areas, but not the entire picture.

In some embodiments, the dedicated memory to store reference samples ofpreviously coded CUs for future intra block copy reference is referredto as a reference sample memory. In one example, the memory size is oneCTU, such as for storing up to one previously coded CTU or one left CTU.In another example, the memory size is two CTUs, such as two previouslycoded CTUs or two left CTUs, or one current CTU together with one leftCTU. In some embodiments, each CTU requires a memory size for storing128×128 luma samples, together with corresponding chroma samples. When areference block is outside the stored, reconstructed areas, thereference block cannot be used for IBC.

In some embodiments, when starting a new CTU (i.e., a current CTU), thereference sample memory allocates space for storing the reconstructedsample of the entire current CTU. In some examples, the memory size isone CTU, and the allocated space for the current CTU can still bepartially used to store the reconstructed samples from a previouslycoded CTU, hence the allocation of space for the current CTU is notcompleted at the beginning of the current CTU. Therefore, a portion (orlocation) of the reference sample memory that stores the reconstructedsamples from the previously coded CTU can be used in IBC mode to predicta current coding block in the current CTU until this portion is updatedby the reconstructed samples of the current coding block in the currentCTU. After that, the data in this portion can still be used for IBCreference for providing reconstructed samples from the current CTU, butno longer for providing the reconstructed samples from the previouslycoded CTU that have just been overwritten.

In some embodiments, the current CTU is divided into a number ofpartitions based on one or more predefined grid patterns. For example,into 64×64 partitions, into 32×32 partitions, etc. If the location ofthe current coding block in the current CTU falls into one of thepredefined partitions, this will indicate the reconstructed samples forthe whole corresponding partition stored in the reference sample memorywill be updated with reconstructed samples from the current CTU, and theold reconstructed samples from a previously coded CTU in that partitionin the reference sample memory cannot be used for IBC referencepurposes. In some examples, the partition size is at least as large as alargest possible IBC code block size. For example, if the maximumreference block size for IBC is 64×64, then the CTU can be divided intoas small as 64×64 partitions.

In some alternative embodiments, when a reference block in a previouslycoded CTU and its collocated block in the current CTU share the samelocation in the reference sample memory, the location of memory will beupdated with the data from the current CTU when this collocated block inthe current CTU is coded. During the coding process of the current CTU,for a coding block in IBC mode, its reference block in a previouslycoded CTU is found, whose reference samples are stored in the referencesample memory. For this reference block, if none of the samples in itscollocated block in the current CTU has been coded, the location inreference sample memory has not been updated with the data from thecurrent CTU, and this reference block, which contains reference samplesfrom the previously coded CTU, can still be used for IBC. Otherwise,according to an embodiment, if at least one sample of the collocatedblock in the current CTU has been reconstructed, this reference block inthe previously coded CTU can be indicated as overwritten and cannot beused for IBC reference.

In some embodiments, the memory size is two CTUs. When starting a newCTU (i.e., a current CTU), the reconstructed samples from a mostrecently coded CTU may be left as is, and the allocated space for thecurrent CTU can be partially used to store the reconstructed samplesfrom a previously coded CTU that is coded before the most recently codedCTU. Therefore, depending on the coding order, the block partitioningstructure, and the availability of the reconstructed samples in thememory, the allowable area for reference samples used in IBC mode can beextended to the reconstructed part of the current CTU, the entire mostrecently coded CTU, and/or a portion of the previously coded CTU thatcan be indicated as not overwritten by the reconstructed samples of thecurrent block.

In a different embodiment, the memory size is two CTUs. When starting anew CTU (i.e., a current CTU), the reconstructed samples from a mostrecently coded CTU may be left as is. Therefore, depending on the codingorder, the block partitioning structure, and the availability of thereconstructed samples in the memory, the allowable area for referencesamples used in IBC mode can be extended to the reconstructed part ofthe current CTU and the entire most recently coded CTU.

In some examples, the size of an IBC reference sub-block can be as largeas a regular inter coded block. In order to utilize the reference samplememory more efficiently, the size of an IBC reference sub-block can belimited to not greater than 64 luma samples at either width or heightedge, where corresponding size constraints apply to chroma samples,depending on the color format. For example, in 4:2:0 format, the size ofa chroma block in IBC mode can be limited to not greater than 32 sampleson each side. In some embodiments, lower limits, such as 32 luma sampleseach side can be used.

In the following non-limiting examples, for the purposes of illustratingvarious embodiments, the maximum IBC reference sub-block size is set to64×64 luma samples. Therefore, in a CTU size of 128×128 luma samples,for luma samples, sub-blocks of 128×128, 128×64, 64×128, 128×32, 32×128,etc., cannot use intra block copy mode. For chroma samples, depending onthe color format, similar to the constraints for luma samples, thecorresponding sizes for chroma samples apply.

FIG. 9 is a schematic illustration of a current block (CTU, 910) and aneighboring block (CTU, 960) in a current picture using IBC inaccordance with an embodiment.

In some embodiments, two sub-blocks from different CTUs are referred toas collocated sub-blocks when these two sub-blocks have the same sizeand have a same location offset value relative to an upper-left cornerof the respective CTU. FIG. 9 shows a current sub-block (912) in thecurrent block (i.e., CTU) (910) and three of its possible referencesub-blocks (962, 964, and 966) in a left, previously coded block (960)that are identifiable by respective block vectors (922, 924, and 926).In this example, if the reference sample memory size is one CTU,reference sub-block (966) can be found from the memory because itscollocated sub-block (936) in the current block (910) has not yet beenreconstructed (white area). Therefore the location of the referencesample memory still stores the reference samples from the previouslycoded block (960). On the contrary, reference sub-block (962) cannot beused, as its collocated sub-block (932) in the current block (910) hasbeen reconstructed completed (grey area). The location of referencesample memory for reference sub-block (962) has been overwritten withthe reconstructed samples from the sub-block (932) in the current block(910). Similarly, reference sub-block (964) cannot be a valid referencesub-block, because part of its collocated sub-block (934) in the currentblock (910) has been reconstructed, and therefore that part of thememory has been partially overwritten with the data in the current block(910).

In order to efficiently utilize the stored reconstructed samples whilesharing a memory space between CTUs, an encoder or a decoder candetermine whether a reference sub-block from a previously coded block isoverwritten (or is otherwise considered to be overwritten) based on apartition structure, a coding order, and/or a position of a currentsub-block in a current block.

For example, when a reference sub-block in a previously coded block andits collocated sub-block in the current block share the same location inthe reference sample memory, the location of memory can be indicated asupdated (e.g., overwritten or otherwise considered as overwritten) withthe data in the current block when any part of this collocated sub-blockin the current block is coded. During the coding process of the currentblock, for a sub-block in IBC mode, its reference sub-block in apreviously coded block is found, whose reference samples are stored inthe reference sample memory. For this reference sub-block, if none ofthe samples in its collocated sub-block in the current block has beencoded, the location in reference sample memory has not been updated withthe data from the current block, this reference sub-block, whichcontains reference samples from a previously coded block, can be usedfor IBC reference. Otherwise, when at least one sample of the collocatedsub-block in the current block is coded, the corresponding location inreference sample memory has been updated by the data in the currentblock, and this reference sub-block cannot be used for IBC reference.

The above general solution is based on checking availability ofdifferent locations during the process of encoding and/or decoding acurrent block. Such an availability checking process, in some examples,can be simplified to only checking availabilities at a few pre-setlocations. In some examples, the determination of the availability of a64×64 luma block from the previous coded block can be based on whetherany part of its collocated 64×64 block of the current block has beencoded or not. In this case, only the upper-left position of each 64×64block in the current block may need to be checked. Other positions maybe checked in other embodiments. The proposed methods/solutions can beextended to smaller block sizes, such as the evaluation based on 32×32blocks.

Different determination factors for different partitioning structureswill be further described based on the following two partitioningscenarios. Based on different partitioning structures, such availabilitydetermination may be made with no or limited checking of individualsamples in order to improve IBC performance by increasing the availablereference range without using extra reference sample memory.

Under a first scenario, each of the four 64×64 luma partitions (32×32chroma partition in 4:2:0 format) in the current CTU will be containedcompletely in a coding block (also referred to as a sub-block); or, eachcoding block in the current CTU will be contained completely in one ofthe four 64×64 luma partitions (32×32 chroma partition in 4:2:0 format).

According to the first scenario, at a 128×128 CTU level, this block canbe coded as is (128×128), or split into four 64×64 blocks and with apotential further split, or split into two 128×64 blocks and with apotential further split, or split into two 64×128 blocks and with apotential further split.

In some variations, ternary-tree split for a block with either edge(width or height) larger than 64 luma samples is not allowed; otherwisethe resulting block will not be contained in one of the four 64×64partitions, or contains one of the four 64×64 partitions completely.

In one example, if the coding block is 128×128 in size, and the max IBCblock size is 64×64, then this 128×128 block will not be coded in IBCmode.

In one example, if the coding blocks are four 64×64 blocks, theavailability of reference samples can be illustrated with reference toFIG. 10A.

FIG. 10A is a schematic illustration of how reconstructed samples in aneighboring block are to be indicated as overwritten based on a positionof a current sub-block that is coded using IBC in accordance with oneembodiment.

In FIG. 10A, a current block (1010) corresponds to a current CTU thatincludes four 64×64 partitions (1012, 1014, 1016, and 1018). Apreviously coded block (1060) corresponds to a left CTU that includesfour 64×64 partitions (1062, 1064, 1066, and 1068). The coding order forprocessing coding blocks in the current block (1010) starts from theupper-left partition (1012), then the upper-right partition (1014), thenthe lower-left partition (1016), and finally the lower-right partition(1018). The 64×64 partition with vertical stripes is where the currentcoding block is located (the current coding block can be smaller than64×64 in size). The shaded grey blocks are the reconstructed blocks. Theones marked “X” are not available for IBC reference since they should beor have been overwritten with the reconstructed samples from the currentblock in the corresponding locations.

Therefore, if the current coding block falls into the upper-left 64×64partition (1012) of the current block (1010), then in addition to thealready reconstructed samples in the current CTU, the reconstructedsamples in the upper-right, lower-left, and lower-right 64×64 partitions(1064, 1066, and 1068) of the left CTU (block 1060), can be referencedusing the IBC mode. Partition (1062) is indicated as overwritten andthus unavailable.

If the current block falls into the upper-right 64×64 partition (1014)of the current block (1010), then in addition to the alreadyreconstructed samples in the current CTU, the reconstructed samples inthe lower-left and lower-right 64×64 partitions (1066 and 1068) of theleft CTU (block 1060), can be referenced using the IBC mode in anembodiment. Partitions (1062 and 1064) are indicated as overwritten andthus unavailable.

If the current block falls into the lower-left 64×64 partition (1016) ofthe current block (1010), then in addition to the already reconstructedsamples in the current CTU, the reference samples in the lower-right64×64 partition of the left CTU (block 1060), can be referenced usingthe IBC mode in an embodiment. Partitions (1062, 1064, and 1066) areindicated as overwritten and thus unavailable.

If the current block falls into the lower-right 64×64 partition (1018)of the current block (1010), only the already reconstructed samples inthe current CTU can be referenced using the IBC mode in an embodiment.Partitions (1062, 1064, 1066, and 1068) are indicated as overwritten andthus unavailable.

The above assumption works for the case that the CTU will be split inquad-tree at a first level (if there is any split at 128×128 level),such as when a separate luma/chroma coding tree (dual-tree) is used.

In one example, if the coding blocks are two 128×64 blocks, it is notallowed to apply horizontal binary-tree split at the next level.Otherwise, the resulting 128×32 block will be contained by two 64×64partitions, which violates the assumption under the first scenario.Therefore, each 128×64 block will be coded as is, or split into two64×64 blocks, or may be split by quad-tree into four 64×16 blocks.

In one example, if the coding blocks are two 64×128 blocks, it is notallowed to apply vertical binary-tree split at the next level.Otherwise, the resulting 32×128 block will be contained by two 64×64partitions, which violates the assumption under the first scenario.Therefore, each 64×128 block will be coded as is, or split into two64×64 blocks, or may be split by quad-tree into four 16×64 blocks.

In some examples, the VVC standard allows flexible block partitioningstrategies with quad-tree, binary-tree, and ternary-tree. If the firstlevel split is not quad-tree, it can still be binary-tree split (notternary split), such as when dual-tree is not used. If verticalbinary-tree split is applied at the first level from the CTU, such ashaving two 128×64 blocks or two 64×128 blocks, then the coding order of2nd and 3rd of the four 64×64 partitions in FIG. 10A may be different.

FIG. 10B is a schematic illustration of how reconstructed samples in aneighboring block are to be indicated as overwritten based on a positionof a current sub-block that is coded using IBC in accordance withanother embodiment. In FIG. 10B, the availability of reference samplesfor an upper-right 64×64 partition and a lower-left 64×64 partition areshown, when the vertical binary-tree split is applied at a 128×128 levelfrom the CTU. When the horizontal binary-tree split is applied at a128×128 level from the CTU, the coding order and availability ofreference samples for an upper-right 64×64 block and a lower-left 64×64block are the same as in FIG. 10A.

Therefore, if a current coding block falls into the upper-left 64×64partition (1012) of the current block (1010), then in addition to thealready reconstructed samples in the current CTU, the reconstructedsamples in the upper-right, lower-left, and lower-right 64×64 partitions(1064, 1066, and 1068) of the left CTU (block 1060), can be referencedusing the IBC mode according to an embodiment. Partition (1062) isindicated as overwritten and thus unavailable.

If the current block falls into the lower-left 64×64 partition (1016) ofthe current block (1010), then in addition to the already reconstructedsamples in the current CTU, the reconstructed samples in the upper-rightand lower-right 64×64 partitions (1064 and 1068) of the left CTU (block1060), can be referenced using the IBC mode according to an embodiment.Partitions (1062 and 1066) are indicated as overwritten and thusunavailable.

If the current block falls into the upper-right 64×64 partition (1016)of the current block (1010), then in addition to the alreadyreconstructed samples in the current CTU, the reference samples in thelower-right 64×64 partition of the left CTU (block 1060), can bereferenced using the IBC mode. Partitions (1062, 1064, and 1066) areindicated as overwritten and thus unavailable.

If the current block falls into the lower-right 64×64 partition (1018)of the current block (1010), only the already reconstructed samples inthe current CTU can be referenced using the IBC mode according to anembodiment. Partitions (1062, 1064, 1066, and 1068) are indicated asoverwritten and thus unavailable.

For the discussions with reference to FIG. 10A and FIG. 10B, twoexemplary solutions are summarized as follows.

A first exemplary solution is for fully reusing the reference samplememory when possible. More specifically, depending on the location of acurrent sub-block (e.g., a coding block) relative to a current block(e.g., a CTU), the following can apply:

-   -   If a current sub-block falls into the upper-left 64×64 partition        of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the upper-right, lower-left, and        lower-right 64×64 partitions of the left block, using the IBC        mode.    -   If the current sub-block falls into the upper-right 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the lower-right 64×64 partition of        the left block, using the IBC mode. Also, if luma location        (0, 64) relative to the current block has not yet been        reconstructed, the current sub-block can also refer to the        reconstructed samples in the lower-left 64×64 partition of the        left block, using the IBC mode.    -   If the current sub-block falls into the lower-left 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the lower-right 64×64 partition of        the left block, using the IBC mode. If luma location (64, 0)        relative to the current block has not yet been reconstructed,        the current sub-block can also refer to the reconstructed        samples in the upper-right 64×64 partition of the left block,        using the IBC mode.    -   If the current block falls into the lower-right 64×64 partition        of the current block, it can only refer to the already        reconstructed samples in the current block, using IBC mode.

Table I below summarizes the availabilities of reconstructed samplesfrom a left block for a first exemplary solution. UL, UR, LL, and LRrefer to upper-left, upper-right, lower-left, and lower-right,respectively. Mark “X” means not available, mark “Y” means available.

TABLE I reconstructed sample availability for first exemplary solutionCurrent sample Ref sample in left block in current UL UR LL LR block 64× 64 64 × 64 64 × 64 64 × 64 UL 64 × 64 X Y Y Y UR 64 × 64 X X Y (when(0, Y 64) location is not reconstructed)/ X LL 64 × 64 X Y (when (64, XY 0) location is not reconstructed)/ X LR 64 × 64 X X X X

A second exemplary solution is for a simplified process regardless ofthe adopted block partitioning strategy. More specifically, depending onthe location of a current sub-block (e.g., a coding block) relative to acurrent block (e.g., a CTU), the following can apply:

-   -   If a current sub-block falls into the upper-left 64×64 partition        of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the upper-right, lower-left, and        lower-right 64×64 partitions of the left block, using the IBC        mode.    -   If the current sub-block falls into the upper-right 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the lower-right 64×64 partition of        the left block, using the IBC mode.    -   If the current sub-block falls into the lower-left 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the lower-right 64×64 partition of        the left block, using the IBC mode.    -   If the current block falls into the lower-right 64×64 partition        of the current block, it can only refer to the already        reconstructed samples in the current block, using the IBC mode.

Table II below summarizes the availabilities of reconstructed samplesfrom a left block for a second exemplary solution. UL, UR, LL, and LRrefer to upper-left, upper-right, lower-left, and lower-right,respectively. Mark “X” means not available, mark “Y” means available.

TABLE II reconstructed sample availability for second exemplary solutionCurrent sample Ref sample in left block in current UL UR LL LR block 64× 64 64 × 64 64 × 64 64 × 64 UL 64 × 64 X Y Y Y UR 64 × 64 X X X Y LL 64× 64 X X X Y LR 64 × 64 X X X X

Under a second scenario, at CTU root (128×128 luma samples), only aquad-tree and a binary-tree split is allowed. After that, a binary splitor a ternary split can be applied to either side of each 64×128, 128×64,or 64×64 block.

According to the second scenario, it is only guaranteed that if thecurrent sub-block in CPR mode falls into the upper-left 64×64 partition,then all the coding units in the upper-left 64×64 partition will becoded prior to coding blocks in the lower-right 64×64 partition. In thiscase, the lower-right 64×64 partition of left block has not yet beenupdated while processing coding units in the upper-left 64×64 partitionof current block. Reconstructed samples in this reference area (thelower-right 64×64 partition of left block) can be used for CPRreferencing.

For coding blocks in the other three 64×64 partitions of the currentblock, there is no guarantee that a complete 64×64 partition thatcontains reference samples of the left block will not be updated duringthe processing of coding units in the corresponding 64×64 partitions. Insome examples, no special operation is proposed.

Under the second scenario, two exemplary solutions are summarized asfollows.

A third exemplary solution allows the lower-right 64×64 partition ofleft block to be used as reference for CPR mode, if current sub-block isinside the upper-left 64×64 partition of the current block. Forsub-blocks inside other three 64×64 partitions of the current block,they can only refer to reconstructed samples within the current block.

Table III below summarizes the availabilities of reconstructed samplesfrom a left block for a third exemplary solution. UL, UR, LL, and LRrefer to upper-left, upper-right, lower-left, and lower-right,respectively. Mark “X” means not available, mark “Y” means available.

TABLE III reconstructed sample availability for third exemplary solutionCurrent sample Ref sample in left block in current UL UR LL LR block 64× 64 64 × 64 64 × 64 64 × 64 UL 64 × 64 X X X Y UR 64 × 64 X X X X LL 64× 64 X X X X LR 64 × 64 X X X X

To further improve upon the third exemplary solution, for each sub-blockin the current block, the availability of each 64×64 partition in leftblock can be evaluated by checking the top-left corner's availability ofeach 64×64 partition in the current block. For example, when a currentsub-block is in an upper-right 64×64 partition of the current block, ifthe upper-left corner of the lower-left 64×64 partition in the currentblock has not yet been reconstructed, that means the upper-left andupper-right 64×64 partitions of current block will be processed prior tothe lower-left and lower-right 64×64 partitions of current block. So thereference sample memory locations that store reference samples in thelower-left and lower-right 64×64 partition of the left block have notyet been updated. They can be used as references for the currentsub-block in CPR mode. Similar checks for upper-left corner ofupper-right 64×64 partition will apply.

Accordingly, the fourth exemplary solution allows for more fully reusingthe reference sample memory when possible. More specifically, dependingon the location of the current sub-block relative to the current block,the following can apply:

-   -   If a current sub-block falls into the upper-left 64×64 partition        of the current block, then in addition to the already        reconstructed samples in the current block, it can also refer to        the reconstructed samples in the lower-right 64×64 partition of        the left block, using the IBC mode. Also, if luma location        (0, 64) relative to the current block has not yet been        reconstructed, the current sub-block can also refer to the        reconstructed samples in the lower-left 64×64 partition of the        left block, using the IBC mode. If luma location (64, 0)        relative to the current block has not yet been reconstructed,        the current sub-block can also refer to the reconstructed        samples in the upper-right 64×64 partition of the left block,        using the IBC mode.    -   If the current sub-block falls into the upper-right 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, if luma location        (0, 64) relative to the current block has not yet been        reconstructed, the current sub-block can also refer to the        reconstructed samples in the lower-left 64×64 partition and the        lower-right 64×64 partition of the left block, using the IBC        mode.    -   If the current sub-block falls into the lower-left 64×64        partition of the current block, then in addition to the already        reconstructed samples in the current block, if luma location        (64, 0) relative to the current block has not yet been        reconstructed, the current sub-block can also refer to the        reconstructed samples in the upper-left 64×64 partition and the        lower-right 64×64 partition of the left block, using the IBC        mode.    -   If the current block falls into the lower-right 64×64 partition        of the current block, it can only refer to the already        reconstructed samples in the current block, using the IBC mode.

Table IV below summarizes the availabilities of reconstructed samplesfrom left block for a fourth exemplary solution. UL, UR, LL, and LRrefer to upper-left, upper-right, lower-left, and lower-right,respectively. Mark “X” means not available, mark “Y” means available.

TABLE IV reconstructed sample availability for fourth exemplary solutionCurrent sample Ref sample in left block in current UL UR LL LR block 64× 64 64 × 64 64 × 64 64 × 64 UL 64 × 64 X Y (when (64, Y (when (0, Y 0)location is 64) location is not not reconstructed)/ reconstructed)/ X XUR 64 × 64 X X Y (when (0, Y (when (0, 64) location is 64) location isnot not reconstructed)/ reconstructed)/ X X LL 64 × 64 X Y (when (64, XY (when (64, 0) location is 0) location is not not reconstructed)/reconstructed)/ X X LR 64 × 64 X X X X

In the above discussed solutions, the reconstructed samples in the leftblock are divided into four 64×64 partitions. Each one of the 64×64partitions is considered as a whole unit to determine if reconstructedsamples in this partition can be used in coding a current sub-block inCPR mode. The proposed solutions as discussed above can also beapplicable to finer partitioning settings, such as, to evaluate each32×32 partition in the reference sample memory.

Furthermore, the evaluation of whether a reference sub-block for thecurrent sub-block in IBC mode is in the left block can be done bydetermining whether (a) all the samples in the reference sub-block arefrom the left block; or (b) any reconstructed sample in the referencesub-block is from the left block.

An example of the block vector constraints based on the fourth solutiondiscussed above is used as a non-limiting example illustrated asfollows. Also, in the example illustrated below, a CTU has a size of128×128 and the reference sample memory has a size of storing one CTU.In the following example, there is no chroma interpolation for IBC mode.

In this non-limiting example, assume the following:

-   -   a luma location (xCb, yCb) of the upper-left sample of the        current luma coding block (e.g., current sub-block) relative to        the upper-left luma sample of the current picture,    -   a variable cbWidth specifying the width of the current coding        block in luma samples,    -   a variable cbHeight specifying the height of the current coding        block in luma samples,    -   a variable ctuSize specifying the size (with or height) of        coding tree block (e.g., current block) in luma samples, and    -   a luma block vector (bVx, bVy) for the current luma coding block        in integer accuracy.

Therefore, the upper left location of the current sub-block is (xCb,yCb), the lower right location of the current sub-block is(xCb+cbWidth−1, yCb+cbHeight−1). Also, the upper left location of thereference sub-block is (xCb+bVx, yCb+bVy), and the lower right locationof the reference sub-block is (xCb+bVx+cbWidth−1, yCb+bVy+cbHeight−1).

In this non-limiting example, a valid block vector satisfies thefollowing conditions:

-   -   the entire reference sub-block is reconstructed prior to the        current sub-block,    -   the entire reference sub-block is in the same tile/slice as the        current sub-block,    -   bVx+cbWidth+xCb<=0 or bVy+cbHeight+yCb<=0,    -   (yCb+bVy)/ctuSize=yCb/ctuSize,    -   (yCb+bVy+cbHeight=1)/ctuSize=yCb/ctuSize,    -   (xCb+bVx)/ctuSize>=(xCb/ctuSize)−1, and    -   (xCb+bVx+cbWidth−1)/ctuSize<=xCb/ctuSize.

If (xCb+bVx)/ctuSize equals (xCb/ctuSize)−1, which means at least partof the reference sub-block is in the left block, the followings apply:

-   -   the condition (xCb % ctuSize>=64 && yCb % ctuSize>=64) is not        true,    -   if xCb % ctuSize<64 && yCb % ctuSize<64,        -   if location ((xCb/ctuSize)+64, (yCb/ctuSize)) is not            available (it means the sample in this location has not been            reconstructed), and location ((xCb/ctuSize),            (yCb/ctuSize)+64) is not available, then either (xCb+bVx) %            ctuSize>64 or (yCb+bVy) % ctuSize>64 is true,        -   else if location ((xCb/ctuSize)+64, (yCb/ctuSize)) is not            available, then (xCb+bVx) % ctuSize>64 is true, and        -   else (this means location ((xCb/ctuSize), (yCb/ctuSize)+64)            is not available), (yCb+bVy) % ctuSize>64 is true,    -   if xCb % ctuSize>=64 && xCb % ctuSize<64,        -   the location ((xCb/ctuSize), (yCb/ctuSize)+64) is not            available, and (yCb+bVy) % ctuSize>64 is true, and    -   if xCb % ctuSize<64 && xCb % ctuSize>=64,        -   the location ((xCb/ctuSize)+64, (yCb/ctuSize)) is not            available, and (xCb+bVx) % ctuSize>64 is true.

The proposed solutions as described above can be extended also to otherconfigurations of the reference sample memory. Further, while thedetermination of which reconstructed samples are available is describedabove with respect to certain processing orders and partition size(e.g., left to right, or top to bottom), it is noted that thedetermination can be modified in accordance with other processing ordersand/or partition sizes in other embodiments.

FIG. 11 is a schematic illustration of a current block (CTU, 1110), afirst reference block (CTU, 1160), and a second reference block (CTU,1140) between the current block (CTU, 1110) and the first referenceblock (CTU, 1160) in a current picture using IBC in accordance with anembodiment. FIG. 11 shows a current sub-block (1112) in the currentblock (i.e., CTU) (1110), a first possible reference sub-block (1166) inthe first reference block (1160) that is identifiable by a block vector(1126), and a second possible reference sub-block (1142) in the secondreference block (1140) that is identifiable by a block vector (1122).Because the memory space for storing the reconstructed samples of block(1140) remains intact when generating the reconstructed samples of thecurrent block (1110), all reconstructed samples of the second referenceblock (1140) can be available for determining a reference sub-block forthe current sub-block (1112) in the IBC mode. However, the memory spacefor storing the reconstructed samples of the first reference block(1160) is allocated for storing the reconstructed samples of the currentblock (1110), the availability of the reference sub-block within thefirst reference block (1160) would depend on whether the collocatedblock in the current block (1110) has been reconstructed, in a mannersimilar to those discussed above with reference to FIGS. 9-11.

FIG. 12 shows a flow chart outlining a decoding process (1200) accordingto an embodiment of the disclosure. The process (1200) can be used inthe reconstruction of a block (i.e., a current block) of a picture codedusing IBC mode. In some embodiments, one or more operations areperformed before or after process (1200), and some of the operationsillustrated in FIG. 12 may be reordered or omitted.

In various embodiments, the process (1200) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video decoder (310), (410), or (710), and the like. Insome embodiments, the process (1200) is implemented by softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1200). Theprocess starts at (S1201) and proceeds to (S1210).

At (S1210), reconstructed samples of a reconstructed block of a pictureare stored in a memory. The reconstructed samples of the reconstructedblock are reconstructed according to an encoded video bitstream. In someexamples, the reconstructed block corresponds to the block (960) in FIG.9 or block (1160) in FIG. 11. In some examples, the reconstructedsamples of the reconstructed block can be generated using the system ordecoders illustrated in FIGS. 3, 4, and 7.

At (S1220), whether a current sub-block in a current block of thepicture is to be reconstructed using intra block copy (IBC) based on areference sub-block in the reconstructed block is determined. If it isdetermined that the current sub-block is to be reconstructed using IBC,the process proceeds to (S1230). Otherwise, the current sub-block can bereconstructed using another process, and the process proceeds to (S1299)and terminates for the purposes of coding using IBC mode.

At (S1230), whether the reconstructed samples of the reference sub-blockstored in the memory are overwritten (or otherwise indicated asoverwritten) is determined based on a position of the current sub-block.In some examples, the reconstructed samples of the reference sub-blockstored in the memory are determined as overwritten as described above,for example with reference to FIGS. 9-11. When it is determined that thereconstructed samples of the reference sub-block stored in the memoryare indicated as overwritten, the process proceeds to (S1240).Otherwise, the current sub-block is to be reconstructed without usingthe reconstructed samples of the reference sub-block or by anotherprocess, and the process proceeds to (S1299) and terminates for thepurposes of coding using IBC mode. In some examples, the reconstructedsamples of the reconstructed block can be generated using the system ordecoders illustrated in FIGS. 3, 4, and 7.

At (S1240), the reconstructed samples of the current sub-block aregenerated for output based on the reconstructed samples of the referencesub-block when the reconstructed samples of the reference sub-blockstored in the memory are determined to be indicated as not overwritten.At (S1250), the reconstructed samples of a collocated sub-block in thereconstructed block stored in the memory are overwritten with thegenerated reconstructed samples of the current sub-block. In someexamples, the reconstructed samples of the reconstructed block can begenerated using the system or decoders illustrated in FIGS. 3, 4, and 7.

After (S1250), the process proceeds to (S1299) and terminates.

FIG. 13 shows a flow chart outlining an encoding process (1300)according to an embodiment of the disclosure. The process (1300) can beused to encode a block (i.e., a current block) of a picture using IBCmode. In some embodiments, one or more operations are performed beforeor after process (1300), and some of the operations illustrated in FIG.13 may be reordered or omitted.

In various embodiments, the process (1300) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video encoder (303), (503), or (603), and the like. Insome embodiments, the process (1300) is implemented by softwareinstructions, thus when the processing circuitry executes the softwareinstructions, the processing circuitry performs the process (1300). Theprocess starts at (S1301) and proceeds to (S1310).

At (S1310), reconstructed samples of a reconstructed block of a pictureare stored in a memory. The reconstructed samples of the reconstructedblock are reconstructed according to encoded prediction information. Insome examples, the reconstructed block corresponds to the block (960) inFIG. 9 or block (1160) in FIG. 11. In some examples, the reconstructedsamples of the reconstructed block can be generated using the system orencoders illustrated in FIGS. 3, 5, and 6.

At (S1320), whether a current sub-block in a current block of thepicture is to be coded using intra block copy (IBC) based on a referencesub-block in the reconstructed block is determined. If it is determinedthat the current sub-block is to be coded using IBC, the processproceeds to (S1330). Otherwise, the current sub-block can be coded usinga process not fully described in this disclosure, and the processproceeds to (S1399) and terminates for the purposes of coding using IBCmode.

At (S1330), a range of reconstructed samples stored in the memory thatare not overwritten (or not otherwise indicated as overwritten) isdetermined based on at least a position of the current sub-block. Insome examples, the range of reconstructed samples stored in the memorycan be determined as overwritten or not as illustrated described above,for example with reference to FIGS. 9-11. In some examples, thereconstructed samples of the reconstructed block can be generated usingthe system or encoders illustrated in FIGS. 3, 5, and 6.

At (S1340), a reference sub-block within the range of reconstructedsamples that are not indicated as overwritten is determined. At (S1350),reconstructed samples of the current sub-block are generated based onthe reconstructed samples of the reference sub-block. At (S1360), thereconstructed samples of a collocated sub-block in the reconstructedblock stored in the memory are overwritten with the generatedreconstructed samples of the current sub-block. In some examples, thereconstructed samples of the reconstructed block can be generated usingthe system or encoders illustrated in FIGS. 3, 5, and 6.

After (S1360), the process proceeds to (S1399) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can be also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit-   IBC: Intra Block Copy-   CPR: Current Picture Referencing-   BV: Block Vector-   AMVP: Advanced Motion Vector Prediction-   HEVC SCC: HEVC Screen Content Coding-   DPB: Decoded Picture Buffer

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: storing reconstructed samples of a reconstructed block of apicture in a memory, the reconstructed samples of the reconstructedblock being reconstructed according to an encoded video bitstream; andwhen a current sub-block in a current block of the picture is to bereconstructed using intra block copy (IBC) based on a referencesub-block in the reconstructed block, identifying the referencesub-block for the current sub-block: after the reference sub-block isidentified, determining whether the reconstructed samples of thereference sub-block stored in the memory are indicated as overwrittenbased on a position of the current sub-block, generating reconstructedsamples of the current sub-block for output based on the reconstructedsamples of the reference sub-block when the reconstructed samples of thereference sub-block stored in the memory are determined to be indicatedas not overwritten, and overwriting the reconstructed samples of acollocated sub-block in the reconstructed block stored in the memorywith the generated reconstructed samples of the current sub-block. 2.The method of claim 1, wherein the current block includes one or morenon-overlapping partitions, including a current partition in which thecurrent sub-block is located, the reconstructed block includes one ormore non-overlapping partitions that are collocated with the one or morepartitions of the current block, respectively, and the determiningincludes determining the reconstructed samples of the referencesub-block stored in the memory are indicated as not overwritten, whenthe partition in the reconstructed block that includes the referencesub-block is collocated with one of the partitions in the current blockthat has not been reconstructed.
 3. The method of claim 2, wherein thedetermining is performed based on a decoding order of the one or morenon-overlapping partitions in the current block.
 4. The method of claim2, wherein the current block has a size of 128×128 luma samples, and theone or more partitions of the current block includes four partitionseach having a size of 64×64 luma samples.
 5. The method of claim 2,wherein the one or more partitions of the current block includes onlyone partition that is a size of the current block.
 6. The method ofclaim 2, wherein each of the one or more partitions of the current blockhas a size that is equal to or greater than a maximum referencesub-block size used in the IBC.
 7. The method of claim 1, wherein thecurrent block includes upper-left, upper-right, lower-left, andlower-right partitions, the reconstructed block includes upper-left,upper-right, lower-left, and lower-right partitions, and the determiningincludes determining the reconstructed samples of the referencesub-block stored in the memory are indicated as not overwritten when thecurrent sub-block is located in the upper-left partition in the currentblock, and the reference sub-block is located in one of the upper-right,lower-left, and lower-right partitions in the reconstructed block. 8.The method of claim 7, wherein the determining further includesdetermining the reconstructed samples of the reference sub-block storedin the memory are indicated as not overwritten when the currentsub-block is located in the one of the upper-left, upper-right, andlower-left partitions in the current block, and the reference sub-blockis located in the lower-right partition in the reconstructed block. 9.The method of claim 7, wherein the determining further includes:determining the reconstructed samples of the reference sub-block storedin the memory are indicated as not overwritten when the currentsub-block is located in the upper-right partition in the current block,the reference sub-block is located in the lower-left partition in thereconstructed block, and no reconstructed sample in the lower-leftpartition in the current block has been generated; and determining thereconstructed samples of the reference sub-block stored in the memoryare indicated as not overwritten when the current sub-block is locatedin the lower-left partition in the current block, the referencesub-block is located in the upper-right partition in the reconstructedblock, and no reconstructed sample in the upper-right partition in thecurrent block has been generated.
 10. The method of claim 7, wherein thedetermining further includes: determining the reconstructed samples ofthe reference sub-block stored in the memory are indicated as notoverwritten only when the current sub-block is located in the upper-leftpartition in the current block, and the reference sub-block is locatedin the lower-right partition in the reconstructed block.
 11. The methodof claim 1, further comprising: generating the reconstructed samples ofthe current sub-block without using the reference sub-block, when thereconstructed samples of the reference sub-block stored in the memoryare determined to be indicated as overwritten.
 12. An apparatus,comprising: processing circuitry configured to: store reconstructedsamples of a reconstructed block of a picture in a memory, thereconstructed samples of the reconstructed block being reconstructedaccording to an encoded video bitstream; and when a current sub-block ina current block of the picture is to be reconstructed using intra blockcopy (IBC) based on a reference sub-block in the reconstructed block,identify the reference sub-block for the current sub-block; after thereference sub-block is identified, determine whether the reconstructedsamples of the reference sub-block stored in the memory are indicated asoverwritten based on a position of the current sub-block, generatereconstructed samples of the current sub-block for output based on thereconstructed samples of the reference sub-block when the reconstructedsamples of the reference sub-block stored in the memory are determinedto be indicated as not overwritten, and overwrite the reconstructedsamples of a collocated sub-block in the reconstructed block stored inthe memory with the generated reconstructed samples of the currentsub-block.
 13. The apparatus of claim 12, wherein the current blockincludes one or more non-overlapping partitions, including a currentpartition in which the current sub-block is located, the reconstructedblock includes one or more non-overlapping partitions that arecollocated with the one or more partitions of the current block,respectively, and the processing circuitry is further configured todetermine the reconstructed samples of the reference sub-block stored inthe memory are indicated as not overwritten, when the partition in thereconstructed block that includes the reference sub-block is collocatedwith one of the partitions in the current block that has not beenreconstructed.
 14. The apparatus of claim 13, wherein the current blockhas a size of 128×128 luma samples, and the one or more partitions ofthe current block includes four partitions each having a size of 64×64luma samples.
 15. The apparatus of claim 12, wherein the current blockincludes upper-left, upper-right, lower-left, and lower-rightpartitions, the reconstructed block includes upper-left, upper-right,lower-left, and lower-right partitions, and the processing circuitry isfurther configured to determine the reconstructed samples of thereference sub-block stored in the memory are indicated as notoverwritten when the current sub-block is located in the upper-leftpartition in the current block, and the reference sub-block is locatedin one of the upper-right, lower-left, and lower-right partitions in thereconstructed block.
 16. The apparatus of claim 15, wherein theprocessing circuitry is further configured to determine thereconstructed samples of the reference sub-block stored in the memoryare indicated as not overwritten when the current sub-block is locatedin the one of the upper-left, upper-right, and lower-left partitions inthe current block, and the reference sub-block is located in thelower-right partition in the reconstructed block.
 17. A non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding causes the computer to perform: storingreconstructed samples of a reconstructed block of a picture in a memory,the reconstructed samples of the reconstructed block being reconstructedaccording to an encoded video bitstream; and when a current sub-block ina current block of the picture is to be reconstructed using intra blockcopy (IBC) based on a reference sub-block in the reconstructed block,identifying the reference sub-block for the current sub-block; after thereference sub-block is identified, determining whether the reconstructedsamples of the reference sub-block stored in the memory are indicated asoverwritten based on a position of the current sub-block, generatingreconstructed samples of the current sub-block for output based on thereconstructed samples of the reference sub-block when the reconstructedsamples of the reference sub-block stored in the memory are determinedto be indicated as not overwritten, and overwriting the reconstructedsamples of a collocated sub-block in the reconstructed block stored inthe memory with the generated reconstructed samples of the currentsub-block.
 18. The non-transitory computer-readable medium of claim 17,wherein the current block includes one or more non-overlappingpartitions, including a current partition in which the current sub-blockis located, the reconstructed block includes one or more non-overlappingpartitions that are collocated with the one or more partitions of thecurrent block, respectively, and the determining includes determiningthe reconstructed samples of the reference sub-block stored in thememory are indicated as not overwritten, when the partition in thereconstructed block that includes the reference sub-block is collocatedwith one of the partitions in the current block that has not beenreconstructed.
 19. The non-transitory computer-readable medium of claim18, wherein the current block has a size of 128×128 luma samples, andthe one or more partitions of the current block includes four partitionseach having a size of 64×64 luma samples.
 20. The non-transitorycomputer-readable medium of claim 17, wherein the current block includesupper-left, upper-right, lower-left, and lower-right partitions, thereconstructed block includes upper-left, upper-right, lower-left, andlower-right partitions, and the determining includes determining thereconstructed samples of the reference sub-block stored in the memoryare indicated as not overwritten when the current sub-block is locatedin the upper-left partition in the current block, and the referencesub-block is located in one of the upper-right, lower-left, andlower-right partitions in the reconstructed block.